During en estimation meeting it happens that the team agrees that an issue should not be fixed. It could be that it was already included in another issue, that it was based on a misundertanding or that it is simply decided that it is not worth the (estimated) effort.
In such cases the issue will not be added to a sprint, but the fact that it even existed could still be of some value and deleting it is not the right thing to do. It would be best to simply resolve it (with "Won't fix" for example). How can this be done directly on the issue while it is still just living on the backlog?